Associations of objectively measured physical activity, sedentary time and cardiorespiratory fitness with adipose tissue insulin resistance and ectopic fat

Background/objectives Inadequate movement, excess adiposity, and insulin resistance augment cardiometabolic risk. This study examined the associations of objectively measured moderate-to-vigorous intensity physical activity (MVPA), sedentary time and cardiorespiratory fitness (CRF), with adipose tissue insulin resistance and ectopic fat. 

Methods Data were combined from two previous experimental studies with community volunteers (n=141, male=60%, median (interquartile range) age=37 (19) years, body mass index (BMI)=26.1 (6.3) kg·m-2). Adipose tissue insulin resistance was assessed using the adipose tissue insulin resistance index (Adipo-IR); whilst magnetic resonance imaging (MRI) was used to measure liver, visceral (VAT) and subcutaneous abdominal adipose tissue (ScAT). Sedentary time and MVPA were measured via an ActiGraph GT3X+ accelerometer. Generalized linear models examined the association of CRF, MVPA, and sedentary time with Adipo-IR and fat depots. Interaction terms explored the moderating influence of age, sex, BMI and CRF. 

Results After controlling for BMI and cardiometabolic variables, sedentary time was positively associated with Adipo-IR (β=0.68 AU [95%CI=0.27 to 1.10], P<0.001). The association between sedentary time and Adipo-IR was moderated by age, CRF and BMI; such that it was stronger in individuals who were older, had lower CRF and had a higher BMI. Sedentary time was also positively associated with VAT (β=0.05 L [95%CI=0.01 to 0.08], P=0.005) with the relationship being stronger in females than males. CRF was inversely associated with VAT (β=-0.02 L [95%CI=-0.04 to -0.01], P=0.003) and ScAT (β=-0.10 L [95%CI=-0.13 to -0.06], P<0.001); with sex and BMI moderating the strength of associations with VAT and ScAT, respectively. 

Conclusions Sedentary time is positively associated with adipose tissue insulin resistance which regulates lipogenesis and lipolysis. CRF is independently related to central fat storage which is a key risk factor for cardiometabolic disease.